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.Dd July 29, 2011
.Dt ILOGB 3
.Os
.Sh NAME
.Nm ilogb ,
.Nm ilogbf ,
.Nm ilogbl
.Nd an unbiased exponent
.Sh LIBRARY
.Lb libm
.Sh SYNOPSIS
.In math.h
.Ft int
.Fn ilogb "double x"
.Ft int
.Fn ilogbf "float x"
.Ft int
.Fn ilogbl "long double x"
.Sh DESCRIPTION
The
.Fn ilogb ,
.Fn ilogbf ,
and
.Fn ilogbl
functions return the exponent of the non-zero real floating-point number
.Fa x
as a signed integer value.
Formally the return value is the integral part of
.Bd -ragged -offset indent
log_r |
.Va x | ,
.Ed
.Pp
where
.Fa r
is the radix of the machine's floating-point arithmetic defined by the
.Dv FLT_RADIX
constant in
.In float.h .
.Sh RETURN VALUES
As described above, upon successful completion,
the functions return the exponent.
Functionally this is the same as calling the corresponding
.Xr logb 3
function and casting the return value to
.Vt int .
.Pp
The following special cases may occur:
.Bl -enum -offset indent
.It
If
.Fa x
is zero, the value of
.Dv FP_ILOGB0
is returned and a domain error occurs.
.It
If
.Fa x
is infinite, a domain error occurs and the value of
.Dv INT_MAX
is returned.
.It
If
.Fa x
is \*(Na, a domain error is raised and the value of
.Dv FP_ILOGBNAN
is returned.
.It
If the correct value is outside the range of the return type,
a domain error occurs but an unspecified value is returned.
.El
.Sh SEE ALSO
.Xr ilog2 3 ,
.Xr logb 3 ,
.Xr math 3
.Sh STANDARDS
The described functions conform to
.St -isoC-99 .
.Sh BUGS
Neither
.Dv FP_ILOGB0
nor
.Dv FP_ILOGBNAN
is defined currently in
.Nx .
